Stop valves for use in shutting off the flow of fluid through a pipe or diverting a fluid flow from a first pipe to a second pipe are well known. An example is disclosed in U.S. Pat. No. 3,342,453 to Soila et al., which patent is hereby incorporated by reference. The Soila patent discloses a stop valve comprising a valve body defining a mainly cylindrical valve cavity having two or more through passages. A shutter disposed within the valve cavity can be rotated to seal the through passage openings by means of a rotatable turning spindle accessible from the exterior of the valve housing. The shutter is tightened by means of a wedge plug bearing against a corresponding inclined plane on the shutter assembly; as the wedge plug is advanced into the turning spindle, the stopping member is wedged against the corresponding valve seat. The arrangement described in the Soila patent is suitable for use in either two-way or three-way valves.
Problems arise, however, when attempting to use a valve of the type described in the Soila patent in hygienic environments. For example, such valves are frequently needed in dairy processing plants, either as shutoff valves for milk storage tanks or as diverter valves, for diverting the output from a milk storage tank to either of two processing lines or for selecting from between two storage tanks for output to a single processing line. If the valve is not properly seated, milk can leak past the stopping member and settle in the pipe downline of the valve. Since the lines are not refrigerated, the leaked milk can spoil and contaminate the next milk which flows through the line. In addition, if the valve is not properly seated, non-potable CIP ("clean-in-place") solution used to clean lines can leak into the tank and contaminate the milk in the storage tank. However, since it is difficult, if not impossible, to verify that valves of the type disclosed in the aforementioned Soila patent are properly seated by visually inspecting the valve, it is not easy to detect leaks of the type described. Thus, there is a need for a stop valve of the type disclosed in the aforementioned Soila patent which permits easy visual verification that the valve is properly seated.
A further hygienic problem is presented by the construction of the shutter or stopping element of the valve disclosed in the aforementioned U.S. Pat. No. 3,342,453 to Soila et al. Where such valves are to be used in hygienic environments such as the dairy processing plants to which previous reference has been made, sanitary standards require that there be a smooth, radiused edge in all corners and that abrupt transitions be avoided. Further, crevices and cracks must be strictly avoided to prevent debris and germs from gathering in such locations. However, the construction disclosed in the Soila patent does comprise crevices which milk can penetrate. For example, the stopping element is comprised of a plastic packing ring mounted to a metal fastening plate. The plastic ring and metal fastening plate intersect at a sharp right angle, providing a corner within which debris and germs can gather. The construction disclosed in the Soila patent therefore would not be ideal for such hygienic applications. Thus, there is a need for a stop valve of the general type disclosed in the aforementioned Soila patent which eliminates the sharp right angle corner at the intersection between the shutter and its corresponding carrier member.